For many decades GLS (General Lighting Service) or incandescent lamps have been the first choice for illumination in residential applications. These light sources could easily be dimmed using so called phase-cut dimmers. This has led to a large installed base of such dimmers. These dimmers are designed to work on relatively high loads with a substantial power consumption.
New types of light sources like CFL (Compact Fluorescent Lamp) or LED lamps offer very small loads (typically a factor of 10 less than the equivalent GLS lamp) in combination with a highly nonlinear behavior and a large capacitive impedance due to the presence of EMI (Electro-Magnetic Interference) filter networks. Due to these aspects, LED based lamps and CFL assemblies cannot be dimmed inherently using existing phase-cut dimmers. With advanced electronics it is possible to emulate dimming functionality. However, due to technical/physical limitations, the dimming range as well as the range of supported dimmers and configurations in terms of the number and mix of parallel lamps operated with a particular dimmer is limited. Furthermore, the additional circuits typically lead to increased costs and, in most cases, to additional power losses in the lamp assemblies.